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    Subject[PATCH] perf symbols: Follow .gnu_debuglink section to find separate symbols
    The .gnu_debuglink section is specified to contain the filename of the
    debug info file, as well as a CRC that can be used to validate it.

    This doesn't currently use the checksum and relies on the usual build-id
    matching for validation.

    This provides more context:
    http://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html

    Signed-off-by: Pierre-Loup A. Griffais <pgriffais@nvidia.com>
    Reported-by: Mike Sartain <mikesart@valvesoftware.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    ---
    tools/perf/util/symbol.c | 65 +++++++++++++++++++++++++++++++++++++++++++++-
    tools/perf/util/symbol.h | 1 +
    2 files changed, 65 insertions(+), 1 deletion(-)

    diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
    index 3e2e5ea..4788092 100644
    --- a/tools/perf/util/symbol.c
    +++ b/tools/perf/util/symbol.c
    @@ -1590,11 +1590,62 @@ out:
    return err;
    }

    +static int filename__read_debuglink(const char *filename,
    + char *path, size_t size)
    +{
    + int fd, err = -1;
    + Elf *elf;
    + GElf_Ehdr ehdr;
    + GElf_Shdr shdr;
    + Elf_Data *data;
    + Elf_Scn *sec;
    + Elf_Kind ek;
    +
    + fd = open(filename, O_RDONLY);
    + if (fd < 0)
    + goto out;
    +
    + elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
    + if (elf == NULL) {
    + pr_debug2("%s: cannot read %s ELF file.\n", __func__, filename);
    + goto out_close;
    + }
    +
    + ek = elf_kind(elf);
    + if (ek != ELF_K_ELF)
    + goto out_close;
    +
    + if (gelf_getehdr(elf, &ehdr) == NULL) {
    + pr_err("%s: cannot get elf header.\n", __func__);
    + goto out_close;
    + }
    +
    + sec = elf_section_by_name(elf, &ehdr, &shdr,
    + ".gnu_debuglink", NULL);
    + if (sec == NULL)
    + goto out_close;
    +
    + data = elf_getdata(sec, NULL);
    + if (data == NULL)
    + goto out_close;
    +
    + /* the start of this section is a zero-terminated string */
    + strncpy(path, data->d_buf, size);
    +
    + elf_end(elf);
    +
    +out_close:
    + close(fd);
    +out:
    + return err;
    +}
    +
    char dso__symtab_origin(const struct dso *dso)
    {
    static const char origin[] = {
    [SYMTAB__KALLSYMS] = 'k',
    [SYMTAB__JAVA_JIT] = 'j',
    + [SYMTAB__DEBUGLINK] = 'l',
    [SYMTAB__BUILD_ID_CACHE] = 'B',
    [SYMTAB__FEDORA_DEBUGINFO] = 'f',
    [SYMTAB__UBUNTU_DEBUGINFO] = 'u',
    @@ -1662,10 +1713,22 @@ int dso__load(struct dso *dso, struct map *map, symbol_filter_t filter)
    */
    want_symtab = 1;
    restart:
    - for (dso->symtab_type = SYMTAB__BUILD_ID_CACHE;
    + for (dso->symtab_type = SYMTAB__DEBUGLINK;
    dso->symtab_type != SYMTAB__NOT_FOUND;
    dso->symtab_type++) {
    switch (dso->symtab_type) {
    + case SYMTAB__DEBUGLINK: {
    + char *last_slash;
    + strncpy(name, dso->long_name, size);
    + last_slash = name + dso->long_name_len;
    + while (last_slash && *last_slash != '/')
    + last_slash--;
    + if (last_slash)
    + last_slash++;
    + filename__read_debuglink(dso->long_name, last_slash,
    + size - (last_slash - name));
    + }
    + break;
    case SYMTAB__BUILD_ID_CACHE:
    /* skip the locally configured cache if a symfs is given */
    if (symbol_conf.symfs[0] ||
    diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
    index af0752b..a884b99 100644
    --- a/tools/perf/util/symbol.h
    +++ b/tools/perf/util/symbol.h
    @@ -257,6 +257,7 @@ enum symtab_type {
    SYMTAB__KALLSYMS = 0,
    SYMTAB__GUEST_KALLSYMS,
    SYMTAB__JAVA_JIT,
    + SYMTAB__DEBUGLINK,
    SYMTAB__BUILD_ID_CACHE,
    SYMTAB__FEDORA_DEBUGINFO,
    SYMTAB__UBUNTU_DEBUGINFO,
    --
    1.7.9.5

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